JP5448641B2 - Development device - Google Patents

Description

  The present invention relates to a developing device in which a plurality of conveying members in the longitudinal direction are arranged in a space on one side of a developing container partitioned by a partition, and more specifically, a developer replenished in a space on one side is quickly mixed with a circulating developer. It relates to the structure to be made.

  2. Description of the Related Art Image forming apparatuses that develop an electrostatic image formed on a photoreceptor using a two-component developer containing toner and a carrier are widely used. As shown in FIG. 2, the developing device using the two-component developer is agitated and mixed with the replenished developer while circulating the two-component developer in the developer container (41) to frictionally charge the toner and the carrier. ing. A developer carrier (47) and a supply member (42) are disposed in the first chamber (41b) in the longitudinal direction partitioned by the partition wall of the developer container, and a transport member (43) is disposed in the second chamber (41a). Be placed. The supply member (42) and the transport member (43) transport the developer in the opposite direction of the longitudinal direction, so that the developer circulates in the developing device.

  In recent years, the developing device has been downsized to reduce the amount of developer stored in the developing container (41), while the process speed has been increased in order to increase the productivity of image formation, and the toner consumption per unit time has been reduced. is increasing. As a result, the circulation speed of the developer in the developing container (41) is increased, but in image formation with a large amount of toner consumption (high image ratio), the developer circulating in the developing container (41) is replenished in large quantities. Developer has been replenished. As a result, as shown in FIG. 7, the developer carried on the developer carrying body (47) with insufficient charge amount increased the developer involved in the development of the electrostatic image.

  For this reason, as shown in FIG. 6, an auxiliary stirring member (43c) is provided on the conveying member (43) to improve the mixing performance of the replenishment developer with respect to the circulating two-component developer (Patent Document 1). Further, by making the developer conveyance speed in the second chamber (41a) lower than the conveyance speed in the first chamber (41b), the replenishment developer is mixed with the developer circulating in the second chamber (41a). The charge amount of the replenishment developer is increased by extending the time (Patent Document 2).

  Patent Document 3 discloses a developing device in which two transport members are arranged in the second chamber (41a), and the developer transport speed in the second chamber (41a) is further slower than the developing device of Patent Document 2. Indicated. Here, the two conveying members are arranged horizontally, and the supply developer is rotated in the width direction so as to be wound around the middle of the two second conveying members (43).

Japanese Patent Laid-Open No. 7-13420 JP 2001-154471 A JP 2005-345858 A

  In the developing device disclosed in Patent Document 3, the staying time of the supplied developer in the second chamber (41a) becomes long, but the developer is not mixed into the first chamber (41b) without adequate mixing. May flow in.

  That is, if image formation continues with a low image ratio (low toner consumption), the developer stagnates in the developer container (41) and is stirred for a long time, resulting in deterioration of the developer and reduced fluidity. . Then, when image formation is started in a state where the flowability of the developer is lowered and the image ratio is high (toner consumption is large), the replenishment developer is layered on the circulating developer and sufficiently stirred. In some cases, the second chamber (41a) may pass through without being performed. When a light replenishment developer not including a carrier was deposited on a heavy two-component developer including a carrier, a phenomenon was observed in which the light replenishment developer did not sink into the heavy developer but flowed in a plate shape and slipped upward.

  As a result, a part of the replenishment developer is carried on the developer carrying body (47) without being sufficiently charged by friction and is involved in the development of the electrostatic image. When development is performed with a developer having a large variation in charge amount, unevenness in image density is conspicuous and the quality of the output image is degraded. In addition, when development is performed with a developer having an insufficient charge amount, the developer adheres to a white background portion of the image and a fogged image is generated, or scattering of the developer during image formation increases.

  In the present invention, even if the developer is deteriorated, the electrostatic charge image on the image carrier can be developed with a developer having a sufficiently high charge amount by sufficiently stirring and mixing the supplied developer with a circulating developer. An object is to provide a forming apparatus.

The image forming apparatus according to the present invention includes a developing container partitioned into a first chamber and a second chamber by a partition wall having openings at both ends in the longitudinal direction, and the developer disposed in the first chamber in the longitudinal direction. A supply member that supplies the developer to the developer carrier while being conveyed, a first and second conveyance member that is disposed in the second chamber and conveys the developer in a direction opposite to the supply member, and the opening. it is obtained and a developer replenishing device for replenishing the replenishment developer in the upstream side of the second chamber to the developer circulating in the second chamber and the first chamber through the parts. The second transport member is disposed above the first transport member, and the first transport member and the second transport member rotate in the same rotational direction .

  In the developing device of the present invention, there is no room for the replenishment development to be gathered between the first transport member and the second transport member that are parallel to each other and to accumulate thickly, and the replenishment developer is immediately supplied with the rotation of the upper transport member. Mix in circulating developer.

  In addition, since the first conveying member and the second conveying member work together and the circulated developer is deeply wound in the depth direction of the second chamber, even if the developer deteriorates, the fluidity is transferred to the second chamber. It is difficult to form a developer block that loses the toner. Since the developer replenished in the flow that deeply entrains the developer circulating in the second chamber is thinly entrained and mixed by stirring, mixing and diffusion of the circulating developer and the replenished developer is accelerated.

  Therefore, even if the developer is deteriorated, the electrostatic image on the image carrier can be developed with the developer having a sufficiently high charge amount by sufficiently stirring and mixing the supplied developer with circulation.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is a top view of the internal structure of a developing device. 2 is an explanatory diagram of a configuration of a developing device according to Embodiment 1. FIG. It is explanatory drawing of a structure of a conveyance screw. It is explanatory drawing of a structure of the image development apparatus of a comparative example. FIG. 10 is an explanatory diagram of a toner charge amount distribution in a developing device of a comparative example. It is explanatory drawing of the comparison result of the number of uncharged and the toner charged to reverse polarity. It is explanatory drawing of the measurement result of fog density. FIG. 10 is an explanatory diagram of a configuration of a developing device according to Embodiment 2. FIG. 10 is an explanatory diagram of a configuration of a developing device according to Embodiment 3. It is explanatory drawing of stirring and mixing of the replenishment developer in the developing device of a comparative example. FIG. 10 is an explanatory diagram of a developer conveyance state in a stirring chamber in a developing device of Example 4. FIG. 10 is an explanatory diagram of a developer transport state circulating in a developing container in a developing device according to a third embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is another implementation in which part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the plurality of conveying members are arranged in parallel in the second chamber in which the developer is supplied. It can also be implemented in the form.

  Accordingly, various forms of image forming apparatus having a common developing device, that is, an intermediate transfer type, a recording material conveyance type, a tandem type, a single drum type, a full color, and a monochrome can be implemented. Not only a developing device using a two-component developer but also a developing device in which only a single-component developer consumed by a circulating one-component developer is supplied.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter of the image forming apparatus shown by patent documents 1-3, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of a configuration of the image forming apparatus according to the first embodiment. As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PB are arranged along an intermediate transfer belt 10. is there.

  In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 1Y and is primarily transferred to the intermediate transfer belt 10. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 1M, and is primarily transferred onto the yellow toner image on the intermediate transfer belt 10. In the image forming units PC and PB, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1B, respectively, and similarly, are sequentially transferred to the intermediate transfer belt 10 in a primary transfer.

  The four-color toner images primarily transferred to the intermediate transfer belt 10 are transported to the secondary transfer portion T2 and collectively transferred to the recording material P. The recording material P onto which the four color toner images have been secondarily transferred is heated and pressed by the fixing device 15 to fix the toner image on the surface, and then discharged onto the stacking tray 17 through the discharge roller 16.

  The separation roller 21 separates the recording materials P drawn from the recording material cassette 20 one by one and sends them to the registration rollers 22. The registration roller 22 receives and waits for the recording material P in a stopped state, and sends the recording material P to the secondary transfer portion T2 in time with the toner image on the intermediate transfer belt 10.

  The fixing device 15 presses the pressure roller 15b against the fixing roller 15a provided with a heater to form a heating nip. The recording material P is heated and pressurized in the process of being nipped and conveyed by the heating nip, melts the toner image, and fixes the full-color image on the surface.

  The intermediate transfer belt 10 is supported around a tension roller 12, a drive roller 11, and a counter roller 13, and is driven by the drive roller 11 to rotate in the arrow R2 direction. The secondary transfer roller 14 abuts on the intermediate transfer belt 10 whose inner surface is supported by the opposing roller 13 connected to the ground potential to form a secondary transfer portion T2. By applying a positive DC voltage to the secondary transfer roller 14, the toner image carried on the intermediate transfer belt 10 is secondarily transferred to the recording material P.

  The image forming units PY, PM, PC, and PB are substantially the same except that the color of toner used in the developing devices 4Y, 4M, 4C, and 4B is different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit PY will be described, and the other image forming units PM, PC, and PB will be described by replacing Y at the end of the reference code in the description with M, C, and B.

  The image forming unit PY surrounds the photosensitive drum 1Y and includes a corona charger 2Y, an exposure device 3, a developing device 4Y, a primary transfer roller 5Y, and a cleaning device 7Y. The photosensitive drum 1Y has a negatively charged photosensitive layer formed on the outer peripheral surface of an aluminum cylinder, and rotates in the direction of arrow R1 at a predetermined process speed.

  The corona charger 2Y irradiates the photosensitive drum 1Y with charged particles resulting from corona discharge, and charges the surface of the photosensitive drum 1Y to a uniform negative potential. The exposure device 3 scans, with a rotating mirror, a laser beam obtained by ON-OFF modulation of scanning line image data obtained by developing a yellow color separation image, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1Y.

  As will be described later, the developing device 4Y develops the electrostatic image on the photosensitive drum 1Y using a two-component developer. The primary transfer roller 5 </ b> Y presses the inner surface of the intermediate transfer belt 10 to form a primary transfer portion T <b> 1 between the photosensitive drum 1 </ b> Y and the intermediate transfer belt 10. By applying a positive DC voltage to the primary transfer roller 5Y, the negative toner image carried on the photosensitive drum 1Y is primarily transferred to the intermediate transfer belt 10 passing through the primary transfer portion T1.

  The cleaning device 7Y slides and collects the transfer residual toner adhering to the photosensitive drum 1Y that has passed through the primary transfer portion T1 by sliding the cleaning blade against the photosensitive drum 1Y.

<Example 1>
FIG. 2 is a plan view of the internal structure of the developing device. FIG. 3 is an explanatory diagram of the configuration of the developing device according to the first embodiment. FIG. 4 is an explanatory diagram of the configuration of the conveying screw.

  As shown in FIG. 2, the developing device 4Y stirs and charges the two-component developer in the developing container 41, and supports the charged two-component developer on the developing sleeve 47 in a spiked state. Rub. When the power source D4 applies an oscillating voltage in which an AC voltage is superimposed on a DC voltage to the developing sleeve 47, the electrostatic image (exposed portion) having a positive polarity relative to the developing sleeve 47 is charged to a negative polarity. The toner is transferred and the electrostatic image is reversely developed.

  The developing sleeve 47 is a rotatable non-magnetic metal cylinder, and the surface of the developing sleeve 47 preferably has a surface roughness Rz (10-point average roughness) in the range of 10 to 20 μm. The developing sleeve 47 is rotationally driven by a motor 52, and a developing voltage for forming a developing electric field in the developing region S-Dgap is applied by a power source D4.

  The developer container 41 is partitioned into a first chamber (41a) and a second chamber (41b) by a partition wall 49 having openings 49a and 49b at both ends in the longitudinal direction, thereby forming a developer circulation path. The developing screw 42, which is an example of a supply member, is disposed in the first chamber (41b) and supplies the developer to the developer carrier (47) while transporting the developer in the longitudinal direction. The stirring screw 43, which is an example of the first transport member, is disposed in the second chamber (41a) and transports the developer in the direction opposite to the supply member (42). In the developing container 41, the developer circulates through the first chamber (41b) and the second chamber (41a) through the openings 49a and 49b. The developer is circulated in the second chamber (41a). ) Developer is replenished upstream.

  As shown in FIG. 3, the stirring screw 44, which is an example of a second transport member, is disposed in the second chamber (41 a) at least partially overlapping the first transport member (43) in the height direction. The developer is transported in the same direction as the transport member (43).

  The developing sleeve 47 incorporates a fixed magnet 51 having a plurality of magnetic poles. The fixed magnet 51 built in the developing sleeve 47 has a repulsive pole with adjacent magnetic poles of the same polarity. Here, since the magnetic force does not act between the poles of the repulsion pole, the developer cannot be carried. The developer carried on the developing sleeve 47 finishes the toner consumption by the development, and the developer having a lowered toner density leaves the developing sleeve 47 here. The developer that has left the developing sleeve 47 is conveyed by the developing screw 42, flows into the stirring chamber 41a downstream of the developing chamber 41b, and is supplied with the replenishment developer upstream of the stirring chamber 41a.

  The developing container 41 contains a two-component developer composed of a nonmagnetic toner and a magnetic carrier, and the mixing ratio of the nonmagnetic toner and the magnetic carrier is about 1: 9 by weight. The developing sleeve 47 is disposed so as to be partially exposed from the opening of the developing container 41 on the photosensitive drum 1Y side. The developing container 41 is partitioned by a partition wall 49 into a developing chamber 41b in which the developing sleeve 47 is installed and an agitating chamber 41a for agitating the replenishment developer.

  A developing screw 42 for supplying the developer to the developing sleeve 47 is disposed in the developing chamber 41b, and a stirring screw 43 for stirring the circulating developer and mixing the replenished developer in the stirring chamber 41b. 44 are arranged in an overlapping manner.

  Here, the lower end of the outer diameter of the agitating screw 44 is opposed to the upper end of the outer diameter of the agitating screw 43 arranged below with a gap. The reason is that when the lower end surface of the outer diameter of the stirring screw 44 is disposed below the upper end surface of the outer diameter of the stirring screw 43, a large load is applied to the developer at the portion sandwiched between the stirring screws 43, 44. This is because it is not preferable. This is because the life of the developer is shortened when a large load is applied to the developer.

  The developer stored in the developing container 41 is conveyed to the developing screw 42 and the stirring screws 43 and 44 and circulates between the developing chamber 41b and the stirring chamber 41a. The developing screw 42 and the agitation screws 43 and 44 are formed by providing helical fins 42b, 43b and 44b as conveying members around the rotating shafts 42a, 43a and 44a of the magnetic material. The pitches of the fins 42b, 43b, and 44b were 18 mm, 24 mm, and 24 mm, respectively.

  As shown in FIG. 4, in addition to the helical fins 43b and 44b, the stirring screws 43 and 44 include stirring ribs 43c that protrude in the radial direction from the shafts 43a and 44a and have a predetermined width in the developer transport direction. , 44c are arranged. The agitating ribs 43c and 44c agitate the developer as the rotating shafts 43a and 44a rotate, and mix the developer supplied to the circulating developer.

  As shown in FIG. 2, the developer replenishing device 60 replenishes replenished developer upstream of the second chamber with respect to the developer circulating through the developing chamber 41b and the stirring chamber 41a through the openings 49a and 49b.

  As shown in FIG. 3, a developer replenishing device 60 filled with 100% toner replenishing developer is connected to the upper portion of the developing device 4Y. The developer replenishing device 60 supplies to the developing device 4Y a replenishing developer commensurate with the amount of toner that is consumed during image formation and taken out from the developing device 4Y, and the toner occupies the two-component developer in the developing device 4Y. The weight ratio (toner concentration) is maintained within a predetermined range.

  The control unit 62 executes automatic toner replenishment control (ATR: Auto Toner Replenisher) to control the amount of replenishment developer replenished to the stirring chamber 41a. That is, the control unit 62 calculates the toner consumption for each image formation and controls the motor 63 to control the supply screw so that the replenishment developer corresponding to the toner consumption in the image formation falls from the replenishment port 64. 65 is rotated. Further, the control unit 62 calculates the toner concentration of the developer from the magnetic permeability of the developer detected by the inductance sensor 61 installed in the stirring chamber 41a. Then, the supply screw 65 is rotated by controlling the motor 63 so as to converge to a predetermined toner density.

  As a result, the replenishment developer is supplied from the replenishing port 64 upstream of the stirring chamber 41 a to the stirring chamber 41 a and dispersed by the stirring screw 44. The replenishment developer dispersed and taken into the existing circulating developer is mixed in the depth direction by the stirring screw 43. Thereby, the toner concentration in the circulating developer is made uniform.

  The stirring screw 44 installed in the stirring chamber 41a has a function of dispersing the replenishment developer in the developer circulating in the developing container 41. Since the number of revolutions of the stirring screw 44 per minute is set lower than that of the stirring screw 43, the dispersion / mixing ability of the replenishment developer is increased, and development is performed without taking in the replenishment developer into the developer circulating in the developing container 41. It is possible to prevent the agent surface from sliding without being mixed.

  When the stirring screws 43 and 44 work together to perform sufficient mixing, the number of contact between the replenishment developer and the carrier increases. As a result, the number of uncharged toners due to poor mixing is reduced, and the toner charge amount Q / M distribution is stabilized.

  In this way, a part of the two-component developer containing toner charged to a predetermined charge amount Q / M is carried on the developing sleeve 47. The two-component developer carried on the developing sleeve 47 is carried on the developing sleeve 47 with the magnetic blade 46 regulating the layer thickness to a constant thickness. A two-component developer having a constant thickness carried on the developing sleeve 47 is conveyed to a developing region facing the photosensitive drum 1a. The toner in the two-component developer conveyed to the developing area is transferred to the photosensitive drum 1a by the developing electric field formed between the developing sleeve 47 and the photosensitive drum 1, and the electrostatic image on the photosensitive drum 1a is developed. To do.

<Comparative example>
FIG. 5 is an explanatory diagram of a configuration of a developing device of a comparative example. FIG. 6 is an explanatory diagram of the toner charge amount distribution in the developing device of the comparative example. FIG. 7 is an explanatory diagram of a comparison result of the number of uncharged and oppositely charged toners. FIG. 8 is an explanatory diagram of the measurement result of fog density.

  In the two-component development method using a two-component developer in which a nonmagnetic toner and a magnetic carrier are mixed, toner is supplied from a developer supply device provided separately to the developing device. For this reason, stabilizing the toner concentration of the two-component developer (the ratio of the toner weight to the total weight of the carrier and the toner) is an extremely important factor in stabilizing the image quality of the output image.

  As shown in FIG. 5, in the developing device 4H of the comparative example, the developing container 41 is divided by a partition wall 41c into a developing chamber 41b in which the developing sleeve 47 is installed and an agitating chamber 41a for stirring the replenishment developer. . A developing screw 42 is disposed in the developing chamber 41b, and a stirring screw 43 is disposed in the stirring chamber 41a. The developing screw 42 and the stirring screw 43 are provided substantially horizontally and in parallel, and the developer circulates in the developing chamber 41b and the stirring chamber 41a while being stirred and conveyed in opposite directions. Then, the developer screw 42 and the agitation screw 43 convey the developer and circulate it in the developing container 41, so that the replenished developer replenished from the developer replenishing device 60 is mixed with the circulating developer and is added to the toner. Make the concentration uniform.

  As shown in FIG. 2, the replenished developer replenished from the developer replenishing device 60 is conveyed along with the developer circulation by the stirring screw 43 and dispersed in the circulating developer. For this reason, the circulation of the developer plays a very important role in order to disperse the replenishment developer and keep the toner concentration in the developing container 41 constant.

  The toner concentration in the developer changes depending on the developing action and replenishment operation. In order to keep the image quality of the output image constant, it is desirable that the toner density be sufficiently uniform when the replenishment developer is supplied to the developing chamber 41b. For that purpose, it is important that the toner density fluctuations accompanying toner consumption and replenishment developer replenishment are sufficiently stirred in the agitating chamber 41a and flowed into the developing chamber 41b with the toner concentration kept constant.

  However, when the toner concentration of the developer varies significantly, the replenishment developer is not sufficiently stirred and mixed with the circulating developer, resulting in uneven image density and uncharged toner with a low charge amount. Problems occur.

  In particular, with the recent increase in process speed, the amount of toner consumed per unit time tends to increase. At that time, if the rotation speed of the agitation screw 43 is increased as the process speed is increased, the replenishment developer may be transported on the developer surface without being taken into the circulating developer. is there. In this case, there is a problem that the replenishment developer flows into the developing chamber 41b without being stirred and mixed with the circulating developer.

  If the toner concentration fluctuation due to toner consumption and replenishment of the developer cannot be suppressed in the stirring chamber 41a due to insufficient mixing, the distribution of the charge amount Q / M per unit mass of the toner becomes unstable and uncharged. The number of toners increases.

  As shown in FIG. 5, the developing device 4 </ b> H of the comparative example is a conventional developing device that transports the developer in the stirring chamber 41 a using only the stirring screw 43. The amount of developer per minute conveyed through the agitating chamber 41a by increasing the number of revolutions per minute of the agitating screw 43 is set equal to that in the first embodiment. Other parts are the same as those of the first embodiment shown in FIG.

  Then, with respect to the developing device 4Y of Example 1 and the developing device 4H of the comparative example, an endurance experiment of continuous image formation with the same conditions is performed to measure and compare the charge amount of the developer, and at the same time, the quality of the output image is determined. Compared.

  The developing device 4H of the comparative example and the developing device 4Y of the first embodiment are respectively mounted on the image forming apparatus 100 shown in FIG. 1, and the two-component developer and the replenishment developer produced at one time are respectively developed in the developing devices 4H and 4Y. Filled separately. The durability experiment was started by leaving it for 10 hours in an environment of low temperature and low humidity (LL: 23 ° C./5%) where the replenishment developer is difficult to disperse and mix.

  In the durability experiment, 6000 sheets of the entire surface maximum density image having the largest toner consumption (replenishment developer replenishment amount) were continuously printed. The fog density was measured every 1000 sheets, and the toner charge amount distribution was measured after printing 6000 sheets.

  For the fog density measurement, REFECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku was used, and the fog density (%) was calculated from the difference between the whiteness of the white portion of the printed fixed image and the whiteness of the recording material.

  The toner charge amount distribution was measured using an E-Spart Analyzer manufactured by Hosokawa Micron Corporation, and the number (frequency) of toner charge amount increments was measured for 3000 toners.

  FIG. 6 shows the result of measuring the toner charge amount distribution of the developer after the continuous image formation of 6000 sheets.

  As shown in FIG. 6, when the developing device 4H of the comparative example is used, the replenishment developer is not sufficiently mixed and stirred with the carrier in the circulating developer. As shown, there are many toners that are hardly charged. On the other hand, in the developing device 4Y of Example 1, the charge amount of the charge amount distribution is generally increased as compared with the developing device 4H of the comparative example, and the peak in the vicinity of the charge amount 0 is eliminated.

  FIG. 7 shows the result of counting the number of toners charged to the opposite polarity (toner charged to positive polarity) considered to be the cause of the fogged image with respect to 3000 toners. This numerical value is obtained by data processing of the toner charge amount distribution measurement data in FIG. 6 and the number of positively charged toners with a charge amount of 0 μC / g.

  As shown in FIG. 7, when the developing device 4H of the comparative example is used, the number of reversely charged toners is about 307. On the other hand, when the developing device 4Y of Example 1 is used, the number of reversely charged toners is greatly reduced to 230.

  From the results of FIGS. 6 and 7, it can be seen that the use of the developing device 4Y of Example 1 improved the mixing and stirring performance of the replenishment developer and the circulating developer with respect to the developing device 4H of the comparative example.

  FIG. 8 shows the measurement results of printing the entire white background image after 1000 image formations and measuring the fog density. The fog density indicates that the smaller the numerical value, the smaller the toner adhesion amount on the white background portion of the image.

  As shown in FIG. 8, immediately after starting the durability experiment by leaving it in a room temperature and low humidity (NN: 23 ° C./5%) environment for 10 hours, the developing device 4H of the comparative example and the developing device 4e of Example 1 were fogged. The concentration was equivalent to 0.75%.

  Next, printing of the maximum density image on the entire surface was continued, and the fog density was measured again at 1000 sheets. As a result, in the developing device 4H of the comparative example, the fog density is 3.0% and the fog image on the image becomes conspicuous. It was. On the other hand, in the developing device 4e of Example 1, the fog density is increased from 0.75% to 1.7%, but the fog image is not noticeable as in the developing device 4H of the comparative example. It was a good result. Subsequently, a total of 6000 images were formed, and the fog measurement was performed every 1000 sheets. As a whole, the developing device of Example 1 gave better results than the developing device 4Y of the comparative example.

  As described above, the developing device 4Y according to the first exemplary embodiment has a sufficient stirring and mixing capability between the replenishment developer and the circulating developer, thereby preventing an image problem that occurs due to insufficient toner charge amount. Thereby, it is possible to realize a developing device using a two-component developing system that maintains the initial output image quality over a long period of time.

  Further, in the developing device 4Y according to the first embodiment, by arranging the stirring screws 43 and 44 so as to overlap each other in the height direction, the thickness of the stirring chamber 41a can be made smaller than that when the stirring screws 41 and 44 are arranged horizontally, and the developing device 4Y can be downsized. . Even if the diameter of the stirring screw 43 is not increased, the amount of the developer in the developing container 41 can be increased, and the fluctuation range of the toner density can be reduced.

  Today, development of a developing apparatus is required to be downsized as the entire image forming apparatus is downsized. As shown in FIG. 1, when the yellow (Y), magenta (M), cyan (C), and black (Bk) image forming portions PY, PM, PC, and PB are arranged side by side in the horizontal direction, Narrowing the width of the surface contributes to downsizing of the image forming apparatus. Therefore, as shown in Patent Document 3, it is often impossible in practice to arrange two stirring screws horizontally in the stirring chamber.

<Example 2>
FIG. 9 is an explanatory diagram of a configuration of the developing device according to the second embodiment.

  As shown in FIG. 9, in the developing device of Example 2, the stirring screw 48 is disposed further above the stirring screw 44, and the stirring screws 43, 44, and 48 convey the developer in the stirring chamber 41a in parallel. To do. The replenishment developer supplied to the stirring chamber 41a is sufficiently mixed and stirred in the stirring chamber 41a by the stirring screw 48.

  In the second embodiment, a plurality of conveying members are provided in parallel in the stirring chamber 41a in order to improve the dispersion / mixing ability of the replenishment developer in the stirring chamber 41a. In the stirring chamber 41a, the upper conveying member is responsible for taking in and mixing the replenishment developer with respect to the circulating developer, and the bottom conveying member is responsible for conveying the circulating developer in the axial direction. By carrying out such functional separation of the conveying member, the developer stirring ability and conveying ability are simultaneously improved. With the configuration of the second embodiment, toner density fluctuations associated with toner consumption and replenishment of developer can be relatively suppressed, and density unevenness of the output image can be reduced. In addition, since fluctuations in toner density can be suppressed in the stirring chamber 41a, uncharged toner can be reduced, and occurrence of image defects such as scattering and fogging images can be suppressed.

<Example 3>
FIG. 10 is an explanatory diagram of the configuration of the developing device according to the third embodiment. FIG. 11 is an explanatory view of stirring and mixing of the replenishment developer in the developing device of the comparative example.

  In the developing device of Example 3, in the developing device 4Y of Example 1 shown in FIG. 3, the rotation direction of the conveying screw 44 disposed on the upper side of the stirring chamber 41a is opposite to that of Example 1, but other than that The configuration is the same as that of the first embodiment. For this reason, in FIG. 10, FIG. 11, the code | symbol common to FIG. 3 is attached | subjected to the structural member which is common in Example 1, and the overlapping description regarding a structural member is abbreviate | omitted.

  As shown in FIG. 10, in Example 3, the stirring screw 43 and the stirring screw 44 rotate in the same rotational direction and rotate in the counter direction on the opposite surface. As a result, the replenishment developer was dispersed and mixed in a shorter time than in Example 1, and a high stirring effect was obtained.

  First, using the developing device 4H of the comparative example shown in FIG. 5, the state of the developer circulating while supplying the replenishment developer to the stirring chamber 41a was observed. With the cyan developer circulated, the yellow replenishment developer was replenished, and the toner dispersion / stirring performance was confirmed by high-speed video shooting. Then, as shown in FIG. 11, the developer circulating in the stirring chamber 41 a circulated in the cross-sectional direction of the screw shaft 43 a along with the rotation direction of the fins 43 b of the stirring screw 43 as indicated by the arrows in the figure. It was observed that the replenishment developer was taken into the circulating developer as it was circulated and stirred.

  As shown in FIG. 10, when the stirring screws 43 and 44 are rotated in the same rotational direction, the replenishment developer taken into the developer circulating by the rotation of the stirring screw 44 is rotated around the fins 44b as shown by the arrow D. Then, it is carried below the stirring chamber 41a. In the vicinity of the lower end of the agitating screw 44, it is carried in the direction indicated by the arrow E. Subsequently, it is rotated in the direction indicated by the arrow F at the upper end of the fin 43b of the agitating screw 43. As a result, the replenishment developer circulates around the inner wall of the container of the agitating chamber 41a greatly in the depth direction. Conversely, as in Example 1, when the agitating screw 43 and the agitating screw 44 rotate in opposite rotation directions and move relative to each other in the width direction on the opposite surface, the replenishment developer is moved to the arrow E of the agitating screw 44. It will be taken around in the direction. For this reason, the high stirring ability in the depth direction as in Example 3 could not be obtained.

  In the developing device 4Y of Example 3, 2 g of yellow replenishment developer was replenished to 200 g of cyan developer, and the dispersion / stirring performance of the replenishment developer was confirmed by high-speed video shooting. As a result, as in Example 1, when the stirring screw 43 and the stirring screw 44 were rotated in opposite directions, it took about 90 seconds for the mixing unevenness to completely disappear. On the other hand, when the stirring screw 43 and the stirring screw 44 have the same rotation direction as in Example 3, the mixing unevenness disappeared in about half of 45 seconds.

  Further, in order to confirm the effect of Example 3, the image formation of 6000 sheets performed in the evaluation of Example 1 was similarly performed. Along with Example 1, FIG. 7 shows a comparison result of the number of uncharged and oppositely charged toners, and FIG. 8 shows a fog density measurement result. As shown in FIG. 7 and FIG. 8, in Example 3, as compared with the developing device 4H of the comparative example, a significant improvement is seen as compared with the case of using the developing device 4Y of Example 1. There is also a slight improvement.

  As described above, the developing device of Example 3 can efficiently stir and mix the developer that circulates the replenishment developer. As a result, it is possible to realize a two-component developing type developing device capable of preventing image problems caused by insufficient toner charge amount and maintaining the image quality of the output image in the initial state over a long period of time.

<Example 4>
FIG. 12 is an explanatory diagram of a developer transport state in the stirring chamber in the developing device of Example 4. FIG. 13 is an explanatory diagram of a state in which the developer circulating in the developing container in the developing device of Embodiment 3 is conveyed. In FIGS. 12 and 13, (a) is shown upside down in order to understand the circulation of the developer in contrast to (b). (A) is a transport state of the developer in the developing chamber, and (b) is a transport state of the developer in the stirring chamber.

  The developing device of Example 4 is different from the developing device 4Y of Example 3 shown in FIGS. 2, 3, and 10 in the pitch of the fins 43b of the conveying screw 43 disposed below the stirring chamber 41a. The other configurations are the same as those of the third embodiment. For this reason, in FIG. 12, the same code | symbol as FIG. 3 is attached | subjected to the structural member which is common in Example 3, and the overlapping description regarding a structural member is abbreviate | omitted.

  As shown in FIG. 12, in Example 4, the 1st conveyance member (43) is comprised so that the conveyance amount per unit time may fall downstream from the upstream of the conveyance direction. The developer transport amount per unit time by the upstream portion of the first transport member (43) is larger than the developer transport amount per unit time by the second transport member (44). The developer transport amount per unit time by the downstream portion of the first transport member (43) is smaller than the developer transport amount per unit time by the second transport member (44).

  Specifically, the pitch on the downstream side in the transport direction of the stirring screw 43 disposed on the bottom side of the stirring chamber 41a is narrower than that on the upstream side. The pitch of the agitating screw 44 arranged on the upper side of the agitating chamber 41a is set to 24 mm as a whole, while the pitch of the agitating screw 43 arranged on the bottom side is 24 mm on the upstream half from the center in the longitudinal direction, on the downstream side. Half of the thickness was 18 mm.

  As a result, a developer flow that rises toward the stirring screw 44 on the downstream side of the stirring screw 43 is formed, and the replenishment developer is dispersed and mixed in a shorter time than in the third embodiment, thereby achieving a high stirring effect. Can now be obtained.

  However, the position where the pitch of the stirring screw 43 is changed is not limited to the center in the longitudinal direction, but is a position from the downstream end to a quarter of the entire length, or a position of up to a third. May be.

  Here, as compared with the developing device of Example 3 shown in FIG. 13, the stirring / mixing state of the developer in the stirring chamber 41 a in Example 4 will be described.

  FIG. 13A shows the state of the developer circulating in the developing chamber 41b as viewed from the developing sleeve 47 side in the developing device of the third embodiment. FIG. 13B shows the state of the developer circulating in the stirring chamber 41a as viewed from the side opposite to FIG.

  As shown in FIG. 13A, in Example 3, the developer in the developing chamber 41b is conveyed from the right to the left in the drawing by the developing screw 42, and the stirring chamber 41a is formed in the opening 49a where the partition wall 49 is interrupted. Flow into. Since the developing screw 42 has a relatively high rotational speed per minute, the conveying speed of the circulating developer is urged fast. When the conveying speed of the developing screw 42 is low, the toner concentration of the developer supplied to the developer carrying member becomes non-uniform in the axial direction of the developer carrying member. In particular, when images with a high image ratio and a large amount of toner consumption are output continuously, uneven image density in the axial direction is likely to occur, and it becomes difficult to form a high-quality output image.

  Therefore, on the downstream side of the developing chamber 41b, the developer interface gradually increases and flows into the stirring chamber 41b from the opening 49a. On the other hand, in the stirring chamber 41a, it is desirable that the developer transport speed in the longitudinal direction is not so high that the replenished developer replenished on the upstream side has a sufficient chance of friction and is increased to the required charge amount. It is desirable that the developer stay in the stirring chamber 41a is lengthened and the developer is supplied to the developing chamber 41b through sufficient stirring and mixing.

  As shown in FIG. 13B, in Example 3, in the longitudinal section of the stirring chamber 41a, the developer flows into the stirring chamber 41a on the near side from the developing chamber 41b on the back side of the paper of the opening 49a. come. The developer that has flowed into the stirring chamber 41a is stirred and conveyed from the left side to the right side in the drawing by the stirring screws 43 and 44 arranged in parallel. Here, the transport amount of the developer per unit time by the stirring screw 43 is larger than the transport amount of the developer by the stirring screw 44 per unit time. Therefore, the developer interface gradually decreases toward the downstream side of the stirring chamber 41a, and flows into the developing chamber 41b through the opening 49b where the partition wall 49 is interrupted.

  As shown in FIG. 12, the developer that flows in from the developing chamber 41b through the opening 41b and is transported near the bottom surface of the stirring chamber 41a is transported downstream as it is by the stirring screw 43 on the bottom side. However, in Example 4, the stirring screw 43 has a lower conveyance amount per unit time in the downstream portion than a conveyance amount per unit time in the upstream portion. In the region A on the downstream side of the developing chamber 41b, the pitch of the agitating screw 43 on the bottom side becomes narrower from 24 mm to 18 mm, so that the conveying speed of the developer in the axial direction decreases. For this reason, the developer conveyed later by the bottom stirring screw 43 is taken up by the upper stirring screw 44 so as to be pushed upward. At that time, the developer conveyed between the bottom stirring screw 43 and the upper stirring screw 44 is mixed and exchanged to cause convection of the developer in the depth direction. By causing convection of the developer in the depth direction, the stirring performance of the replenishment developer and the circulating developer is improved.

  In addition, in order to confirm the effect of Example 4, 6000 images formed in the evaluation of Example 3 were similarly performed. Along with Example 3, FIG. 7 shows a comparison result of the number of uncharged and oppositely charged toners, and FIG. 8 shows a fog density measurement result. As shown in FIGS. 7 and 8, the fourth embodiment is significantly improved compared to the developing device 4H of the comparative example, and of course, compared to the case where the developing device 4Y of the third embodiment is used. There is also a slight improvement.

  As described above, the developing device of Example 4 can efficiently stir and mix the developer that circulates the replenishment developer. As a result, it is possible to realize a two-component developing type developing device capable of preventing image problems caused by insufficient toner charge amount and maintaining the image quality of the output image in the initial state over a long period of time.

  As described above, according to the developing devices of the first to fourth embodiments, replenishment development is performed on the circulating developer as compared with the developing device 4H of the comparative example in which one conveying member is arranged in the stirring chamber 41a. The agent can be efficiently stirred. As a result, local variations in the toner density of the developer due to toner consumption and replenishment of the developer can be eliminated, and the charge amount of the toner involved in development can be stabilized high. As a result, the generation of fog images can be suppressed and the image quality of the output image can be kept constant from the beginning to the end. It is possible to suppress toner scattering during image formation, and to prevent the occurrence of toner stains on the recording material and stains inside the apparatus.

1Y, 1M, 1C, 1B Photosensitive drum 2Y, 2M, 2C, 2B Corona charger 3 Exposure device 4Y, 4M, 4C, 4B Developing device 5Y, 5M, 5C, 5B Primary transfer roller 41 Developer container 41a Stir chamber 41b Developer chamber 42 Development screw 43, 44, 48 Stir screw 46 Magnetic blade 47 Development sleeve (developer carrier)
100 Image forming apparatus

Claims (3)

A developing container partitioned into a first chamber and a second chamber by a partition wall having openings at both ends in the longitudinal direction;
A supply member that is disposed in the first chamber and supplies the developer to the developer carrier while conveying the developer in the longitudinal direction;
First and second transport members that are disposed in the second chamber and transport the developer in a direction opposite to the supply member;
A developer replenishing device that replenishes replenishment developer upstream of the second chamber with respect to the developer circulating through the first chamber and the second chamber through the opening;
The developing device, wherein the second transport member is disposed above the first transport member, and the first transport member and the second transport member rotate in the same rotation direction . A developing container partitioned into a first chamber and a second chamber by a partition wall having openings at both ends in the longitudinal direction;
A supply member that is disposed in the first chamber and supplies the developer to the developer carrier while conveying the developer in the longitudinal direction;
First and second transport members that are disposed in the second chamber and transport the developer in a direction opposite to the supply member;
A developer replenishing device that replenishes replenishment developer upstream of the second chamber with respect to the developer circulating through the first chamber and the second chamber through the opening;
The second transport member is disposed above the first transport member, and the first transport member is configured such that the transport amount per unit time is lower than the upstream side in the transport direction. A developing device. A developing container partitioned into a first chamber and a second chamber by a partition wall having openings at both ends in the longitudinal direction;
A supply member that is disposed in the first chamber and supplies the developer to the developer carrier while conveying the developer in the longitudinal direction;
First and second transport members that are disposed in the second chamber and transport the developer in a direction opposite to the supply member;
A developer replenishing device that replenishes replenishment developer upstream of the second chamber with respect to the developer circulating through the first chamber and the second chamber through the opening;
The second transport member is disposed above the first transport member, and the transport amount per unit time of the developer by the upstream portion of the first transport member is per unit time of the developer by the second transport member. A developing device characterized in that the developer transport amount per unit time by the downstream portion of the first transport member is larger than the transport amount and smaller than the developer transport amount per unit time by the second transport member. .

Images